A traffic signal lamp is used to control vehicles and passengers so that traffic can flow smoothly and both drivers and passengers are safe. Brightness and viewing angle are two important requirements that have to be considered in manufacturing a traffic signal lamp. Most countries require very high brightness and limited viewing angle for traffic signal lamps. In general, there should be no brightness above the horizontal line of a traffic signal lamp. The primary light source of a conventional traffic signal lamp has been an incandescent lamp.
In recent years, light emitting diodes are gradually used to replace the incandescent lamp. However, it has been difficult to design traffic signal lamps illuminated by light emitting diodes to satisfy the brightness and viewing angle requirements. One conventional approach to manufacturing a traffic signal lamp illuminated by light emitting diodes is to use a large number of diodes without adding any lens. Because light is emitted towards all directions from the diodes, the illumination above the horizontal viewing angle is completely wasted. In order to satisfy the brightness, many light emitting diodes are required in this approach.
To reduce the number of light emitting diodes required and limit the viewing angle, some manufacturers have tried to add lenses in front of the light emitting diodes. Nevertheless, it is difficult to design high efficiency lens that can greatly increase the brightness of a traffic signal lamp. Most of the design still requires a fairly large number of light emitting diodes. With some complex lens design, it may require a less number of light emitting diodes. However, complex lens design makes the manufacturing difficult and the cost of a lamp too high.
As described above, the conventional approaches to manufacturing traffic signal lamps can not meet the objectives of saving energy and reducing cost. There is a strong need in designing traffic signal lamps illuminated by light emitting diodes that meet the requirements of high brightness, desired viewing angle, and low power consumption.